#include<stdio.h>
void main()
{
    int n, k = 1;
    float fm = 1.0, fz = 2.0, sum = 0, temp;
    scanf("%d",&n);
    while(k <= n)
	{
        sum = sum + fz / fm;
        temp = fz;
        fz = fz + fm;
        fm = temp;
        k++;
    }
    printf("sum = %f",sum);
}